Pc always prints a space first, followed by three (possibly blank)
characters (``LVd'' above) explained below. Then pc prints the
command number, a number uniquely identifying the command's position
in the sequence of commands since the beginning of the user's
session. Finally, the command itself is printed.

While pc always prints a space first, some historycommands, for
example :pcs and :pe, use the first column of output to delimit a
region of commands or to point to a particular event within a
command.

Here, the two slash characters in the first column are intended to
suggest a bracket delimiting commands 52 through 54. The last
command printed by pcs is always the most recent command, i.e., the
command at :here, and is separated from the rest of the display by
an elipsis if some commands are omitted.

Similarly, the :pecommand will print a particular event within a
command block and will indicate that event by printing a ``>'' in
the first column. The symbol is intended to be an arrow pointing at
the event in question.

using the arrow to indicate the event itself. The slash printed
to connect the command, include-book, with the event, defthm, is
intended to suggest a tree branch indicating that the event is
inferior to (and part of) the command.

The mysterious three characters sometimes preceding a command have
the following interpretations. The first two have to do with the
function symbols introduced by the command and are blank if no
symbols were introduced.

At any time we can classify our function symbols into three disjoint
sets, which we will here name with characters. The ``P''
functions are those in :program mode. The ``L'' functions are
those in :logic mode whose guards have not been verified. The
``V'' functions are those in :logic mode whose guards have
been verified. Note that verify-termination and verify-guards
cause function symbols to be reclassified. If a command introduces
function symbols then the first mysterious character indicates the
class of the symbols at the time of introduction and the second
character indicates the current class of the symbols (if the current
class is different from the introductory class).

Thus, the display

PLd 52 (DEFUN FOO (X) X)

tells us that command 52 introduced a :program function but that
some command after 52 changed its mode to :logic and that the
guards of foo have not been verified. That is, foo's
termination has been verified even though it was not verified as
part of the command that introduced foo. Had a subsequent
command verified the guards of foo, the display would contain a
V where the L is.

The display

P d 52 (DEFUN FOO (X) X)

indicates that foo was introduced in :program mode and still
is in that mode.

The third character indicates the enabled/disabled status of the
runes introduced by the command. If the status character is blank
then all the runes (if any) introduced are enabled. If the status
character is ``D'' then some runes were introduced and they are
all disabled. If the status character is ``d'' then at least
one, but not all, of the runes introduced is disabled. Thus, in the
display

L d 52 (DEFUN FOO (X) X)

we see that some rune introduced by command 52 is disabled. As
noted in the documentation for rune, a defuncommand
introduces many runes, e.g., the axiomatic definition rule,
(:definition fn), the executable counterpart rule,
(:executable-counterpart fn), and type-prescriptions,
(:type-prescription fn). The display above does not say which of
the runes based on foo is disabled, but it does tell us one of
them is; see disabledp for how to obtain the disabled runes for
a given function symbol.